1. Field of the Invention
The invention relates to a process for the preparation of .beta.-ketocarboxylic acid esters starting from acetocarboxylic acid esters and carboxylic acid chlorides.
2. Description of the Related Art
A number of processes are known for the preparation of .beta.-ketoesters. Thus, for example, carboxylic acid esters as the carbonyl component are reacted with CH-acidic carboxylic acid esters to give .beta.-ketocarboxylic acid esters using at least equimolar amounts of bases such as, for example, sodium hydride, sodium amide and alkali metal alcoholates, in an inert solvent. Mixed ester condensation reactions are generally carried out only with formic acid esters as the carbonyl component because otherwise mixed reaction products are formed. However, the yields achieved here are relatively low because the .beta.-ketoester formed in the condensation reaction has a higher reactivity than the starting compounds to be converted, which can lead to numerous secondary reactions. Such preparative processes are described in U.S. Pat. Nos. 2,407,942 and 2,367,632.
Furthermore, German patent document A-2412784 describes the condensation of CH-acidic dialkyl ketones with dialkyl carbonates, using at least equimolar amounts of base, in order to prepare .beta.-ketoesters. However, the process has the disadvantage that highly toxic hexamethylphosphorotriamide (HMPT) has to be used as a solvent in order to achieve good yields.
J. Am. Chem. Soc. 67 , 2198 (1945) describes the acylation of sodium acetoacetic acid esters with carboxylic acid chlorides and the cleavage of the resulting acylacetoacetic acid ester with ammonia or sodium methylate to give the .beta.-ketoester. The yields achieved, however, are only of the order of 30 to 40%.
It is known from British patent document B-1000709 and Helv. 35, 2280(1952) to prepare .beta.-ketoesters by reacting acetoacetic acid esters with carboxylic acid chlorides in the presence of magnesium alcoholates and then cleaving the 2-acylacetoacetic acid ester by hydrolysis. In practice, however, this method also has its difficulties. Thus, for example, the activity of commercially available magnesium alcoholate is inadequate, so that magnesium alcoholate needed for the reaction always has to be freshly prepared, but this requires the use of carbon tetrachloride, which is toxicologically very harmful.
The object was therefore to provide a process for the preparation of .beta.-ketoesters which produces the .beta.-ketoesters in good yields, in a simple and cost-effective manner, starting from readily accessible materials.